1. Field of the Invention
The present invention relates to an ultrasonic probe used for an ultrasonic diagnosis apparatus inserted into a body cavity to observe an internal organ, and in particular to an ultrasonic probe for detecting and transmitting rotational information of an ultrasonic transducer disposed in a tubular member rotatably about an axis thereof through an optical fiber.
2. Description of the Prior Art
As the ultrasonic diagnosis apparatus inserted into a body cavity for observation of the motion or the texture of an internal organ, an ultrasonic probe of mechanical scanning type is so far known, in Japanese Published and Examined Utility Model Application No. 62-7301, for instance.
FIG. 1 is a cross-sectional view showing the conventional ultrasonic probe. In the drawing, an ultrasonic transducer 3 fitted to an ultrasonic scanning member 2 is disposed in an end portion of a flexible cylindrical casing 1. The ultrasonic scanning member 2 is fitted to a rotary axle 4 disposed at an axial center of the cylindrical casing 1 so as to be rotatable together with the rotary axle 4 in the cylindrical casing 1.
Further, a disk 6 having a signal generating surface 5 on which reflecting portions and non-reflecting portions are formed alternately and repeatedly is fixed to this rotary axle 4. The disk 6 rotates together with the rotary axle 4 and therefore together with the ultrasonic transducer 3.
Further, a light emitting optical fiber 7 and a light receiving optical fiber 8 are both arranged along the rotary axle 4 in the vicinity of the inner circumferential surface of the cylindrical casing 1.
The disk 6, the light emitting optical fiber 7 and the light receiving optical fiber 8 constitute a rotational information detecting apparatus for detecting rotational information of the rotary axle 4 such as rotational angles and rotational angular velocity of the rotary axle 4.
On the other hand, an ultrasonic drive signal for driving the ultrasonic transducer 3 and a received ultrasonic signal reflected from a body cavity 10 are transmitted through a signal cable 9 arranged in the rotary axle 4.
In operation, when the ultrasonic probe is inserted into a body cavity, the motion or the texture of the internal organ can be observed by rotating the ultrasonic transducer 3. Here, the ultrasonic transducer 3 is rotated via the ultrasonic scanning member 2 rotated by the rotary axle 4 driven by a motor (not shown).
A light beam is emitted from an end of the light emitting optical fiber 7 to the signal generating surface 5. Since the reflecting portions and the non-reflecting portions are formed alternately and repeatedly on the signal generating surface 5, when the disk 6 rotates, a light beam emitted from the light emitting optical fiber 7 is reflected from the signal generating surface 5 as an optical signal. Here, the optical signal received by an end of the light receiving optical fiber 8 changes in light intensity with respect to time, so that it is possible to detect the rotational information (e.g., the rotational angle and the rotational angular velocity) of the rotary axle on the basis of the received optical signal.
An output terminal of the light receiving optical fiber 8 is connected to a control section of the motor for driving the rotary axle 4. The rotational information detecting apparatus and the control section of the motor for driving the rotary axle 4 are connected so as to form a closed loop, so that the rotational angle and the angular velocity of the rotary axle 4 can be controlled on the basis of the rotational information.
However, the conventional ultrasonic probe involves the following problems:
The optical fiber bundle composed of the light emitting optical fiber 7 and the light receiving optical fiber 8 is arranged in the vicinity of the inner circumferential surface of the cylindrical casing 1; that is, the optical fiber bundle is positioned radially outward away from the rotary axle 4. Therefore, when the ultrasonic probe is inserted into a curved body cavity 10 as shown in FIG. 2, the rate of expansion and contraction of the optical fibers 7 and 8 differs largely according to the curvature direction of the optical fiber bundle, so that there exists a problem in that the optical fibers are damaged or cut off because the expansion and contraction rate of the optical fiber exceeds its allowable range according to the curvature direction.
In addition, since the optical fibers are arranged in the vicinity of the inner circumferential surface of the cylindrical casing 1, the expansion and contraction rate of the optical fibers 7 and 8 is larger than that of the cylindrical casing 1 at its axial center. Therefore, there exists another problem in that the transmission characteristics of the optical signal are subjected to change due to a large distortion generated in the optical fiber, thus it has been difficult to obtain an accurate rotational information of the rotary axle 4.